1. Field of the Invention
The present invention relates to a method of driving an indicator tube.
2. Description of the Prior Art
A so-called AC type PDP (plasma display panel) utilizing wall charges and having a memory function is a two-electrode type plasma display panel in which XY electrodes are respectively disposed on both front and rear glass plates in an opposing fashion. Further, there is proposed a plasma display panel of a three-electrode surface type that is the development of the AC type plasma display panel. FIG. 1 of the accompanying drawings shows a fundamental structure of such conventional plasma display panel of the three-electrode surface type. As shown in FIG. 1, this plasma display panel comprises a first electrode 9 and a second electrode 10 disposed parallelly on the same plane of a front glass plate 5, an insulating layer 12 covering the surfaces of the first and second electrodes 9, 10 and an address electrode 11 formed on a rear glass plate 6 opposing the front glass plate 5, the electrode surface of the address electrode 11 being exposed to the outside. The address electrode 11 and the first electrode 9 constituting an XY matrix, and the second electrode 10 is commonly connected to each of the lines as a memory electrode.
Fundamental operation of this plasma display panel is such that a discharge occurred selectively between the address electrode 11 and the first electrode 9 is held between the first and second electrodes 9 and 10. That is to say, the first electrode 9 functions as both an address and a memory. Let it now be assumed that a memory discharge is continuously carried out between the first and second electrodes 9 and 10 and that wall charges exist on both the first and second electrodes 9, 10. Then, let us consider the case that the memory discharge or the wall charge is erased selectively. To erase the discharge, there is used a so-called self-erasure method in which a potential of the first electrode 9 is held at a proper potential immediately after a discharge was produced between the address electrode 11 and the first electrode 9 by a pulse having a very short duration to thereby erase the wall charge on the first electrode 9.
FIG. 2 is a timing chart of waveforms of driving signals according to the typical conventional driving method. As shown in FIG. 2, in order to accumulate wall charges in all cells, a pulse having a sufficient peak value is applied between the first and second electrodes 9, 10. Also, in order to selectively erase the wall charges, an address pulse is applied between the address electrode 11 and the first electrode 9. A duration of the address pulse is very important because if the duration of the address pulse is too short, an erasure discharge is disabled while if it is too long, the wall charge is accumulated on the first electrode 9 one more time.
To solve the problems encountered with the conventional plasma display panel in which address operation and memory operation are carried out by the same electrode, there has been previously proposed a memory sheet type plasma display panel (see Japanese patent application No. 4-74603 and Japanese patent application No. 3-356127 which claims the right of priority).
FIG. 3 is a perspective view showing a fundamental structure of the plasma display panel of memory sheet type in an exploded fashion. As shown in FIG. 3, the plasma display panel of memory sheet type includes address X and Y electrode groups 1 and 2 formed in an XY matrix fashion and a memory A electrode 3 and a memory B electrode 4 which form a pair of common electrodes. More specifically, as shown in FIG. 3, the address X electrode 1 is made of a transparent conductive material on a front glass plate 5 and the electrode surface thereof is exposed in gas space. The other address Y electrode 2 is disposed on a rear glass plate 6 and the electrode surface thereof is exposed in the gas space similarly. Therefore, the two electrode groups operate as an ordinary DC type plasma display panel in which the address X electrode 1 is used as an anode and the address Y electrode 2 is used as a cathode.
The memory A electrode 3 and the memory B electrode 4 are both made of a single metal plate and have through-holes at the positions corresponding to intersection points of the XY matrix formed by the above-mentioned first address X electrode 1 and second address Y electrode 2. Further, each of the metal plates forming the memory A electrode 3 and the memory B electrode 4 is coated on its whole surface including the inner wall of the through-holes with an insulating layer, such as a glass material or the like.
Fundamental operation of the above plasma display panel is to hold a discharge caused by the address electrode by the two memory A electrode 3 and memory B electrode 4. This memory sheet type plasma display panel is simple in operation similarly to the DC type plasma display panel and also has the same memory function as that of the AC type plasma display panel. Therefore, the memory sheet type plasma display panel is expected as one of promising plasma display panels having a bright picture screen. However, a method for effectively driving the plasma display panel of memory sheet type is not yet proposed.
In the method of driving the conventional three-electrode surface discharge type plasma display panel having the structure in which the address operation and the memory operation are effected by the same electrode, voltages of complex waveforms must be applied to the electrodes at high speed. As a result, a manufacturing cost of circuits is increased and operation thereof become unstable, which is one of the factors that hinder the display apparatus from being put into practical use. Further, a method of effectively driving the aforesaid memory sheet type plasma display panel also is not yet proposed.